Scroll type fluid material handling machines are commonly used to compress, pump, expand or meter fluids. These machines have a pair of scrolls with end plates and spiral wraps that cooperate to form a pair of fluid pockets. The fluid pockets move either toward the center of the end plates or toward the radially outer edge of the end plates depending upon the direction of orbital movement of one scroll relative to the other scroll. The relative orbital movement of one scroll relative to the other scroll can be obtained by rotating both scrolls about axes that are offset from each other or by holding one scroll in a fixed position and driving the other scroll in an orbit relative to the fixed scroll.
Scroll type fluid displacement machines which form fluid pockets and move the pockets toward the center of the scrolls are commonly used to compress fluid. As the fluid pockets move toward the center of the scrolls, the pockets decrease in volume thereby compressing the fluid they contain. The fluid pockets deliver the compressed fluid they contain to a discharge aperture at an elevated pressure near the center of the end plates. Such compressors are useful in various machines including refrigeration systems.
Scroll type compressors can be driven by a dedicated power source which drives only the compressor. When they are driven by a dedicated power source, the power source can be turned off when the compressor is not needed. Other scroll type compressors are driven by power sources that drive driven equipment other than the compressor. An example of such a compressor would be an air conditioning compressor for a vehicle with an electric motor or an internal combustion engine which provides power to propel the vehicle, to steer the vehicle, to brake the vehicle, and to operate other accessories. When a scroll compressor is driven by a power source that provides power for other functions, it is desirable and generally necessary to provide a separate clutch that allows the scroll type compressor to be disconnected when it is not needed. Substantial energy can be saved by disconnecting a compressor when the compressor is not needed.
Clutches for scroll type compressors can take many forms. The most common type clutch used to drive compressors on automotive vehicles are electromagnetic clutches. Electromagnetic clutches are relatively small, compact, reliable and efficient compared to some other clutches. However, an electromagnetic clutch attached to a scroll compressor substantially increases the size and weight of a compressor and drive clutch combination. An electromagnetic clutch is likely to be larger in diameter than a scroll type compressor that it drives. The electromagnetic clutch also increases the length of a clutch and compressor combination. In addition to being physically large, electromagnetic clutches have substantial weight. A lightweight scroll type compressor could weigh less than the electromagnetic clutch which drives it.